SENIOR Coalition MPs have promised to make foreign investment a key election issue as they raise "serious concerns" over a proposed American takeover of the nation's largest publicly listed farm business.

The threat of a political stoush over the issue comes as Prime Minister Julia Gillard yesterday announced a national land register for foreign investment following public unrest about overseas investments in key rural sectors.

Agriculture Minister Joe Ludwig said he wants the national register running by mid-2013, promising it will lead to a more "informed" debate on who owns farm lands and agribusiness assets.

The minister said it was "important" to get all of the facts out on the table.

But the opposition, the Greens and cross-bench MPs said the national register would do little to stem the level of foreign takeovers of Australian agribusinesses.

South Australian Senator Nick Xenophon described the plan as "window dressing" while Greens Senator Rachel Siewert said there was "much more to be done" to ensure greater transparency.

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